The present invention relates generally to active components for suspension systems, and more particularly, to springs for such systems.
A basic object of any suspension system in a vehicle is to suspend the vehicle body above the vehicle wheels. To achieve this end, suspension systems are typically connected between the axle, or its housing, and the vehicle frame. Suspension systems typically include active components, such as springs and the like, to keep the sprung mass (vehicle body) suspended above the unsprung mass (vehicle wheels). A suspension system preferably permits a relatively smooth, yet stable, ride during acceleration, deceleration and cornering of the vehicle, and during jounce and rebound of the axle when the vehicle is driven over bumpy surfaces and the like.
In suspension systems, leaf springs often serve as the active components. In a variety of circumstances, concerns regarding vehicle packaging necessitate the use of an asymmetrical leaf spring. In asymmetrical leaf springs, one cantilever of the leaf spring is longer than the other cantilever. For instance, and referring to FIG. 1, in a typical asymmetrical leaf spring 10, the front cantilever 12 (i.e., that portion of the leaf spring extending from one end 14 of the leaf spring to the center 16 of the axle seat portion 17) might be longer than the rear cantilever 18 (i.e., that portion of the leaf spring extending from the center 16 of the axle seat portion 17 to the opposite end of the leaf spring 20). This difference in length between cantilevers is what classifies a leaf spring as asymmetrical.
Ordinarily, leaf springs in general, including asymmetrical leaf springs, are designed such that they have the same stress level in each cantilever. In the case of asymmetrical leaf springs, this optimized design results in the shorter cantilever being stiffer than the longer cantilever. Stated differently, the shorter cantilever has a higher spring rate than the longer cantilever. Conversely, the longer cantilever is softer than the shorter cantilever, and it has a lower spring rate. Given this optimized design, during deflection of the leaf spring (e.g., during jounce and rebound of the vehicle axle), the seat portion 16 of the spring translates vertically and rotates due to the differing spring rates of the respective cantilevers. This rotation of the seat portion, in turn, applies torsion to the axle and causes it to rotate, producing a varying caster angle during vehicle movement. Those skilled in the art understand that this varying caster angle is sometimes undesirable, and can serve as a drawback designed for optimum stress tolerances. Nevertheless, vehicle packaging concerns and the like often necessitate use of such asymmetrical leaf springs.
In light of these deficiencies of stress tolerant asymmetrical leaf springs, it is desirable to design an asymmetrical leaf spring that has cantilevers with substantially equal spring rates so that the axle has constant caster during jounce and rebound.
When packaging concerns are not present, it is often desirable to use symmetrical leaf springs, such as the symmetrical leaf spring 22 shown in FIG. 2. In such springs, the front and rear cantilevers 24, 26 are substantially equal in length. When optimized for maximum stress tolerance, the cantilevers not only have equal stress levels, but also have equal spring rates to yield the equal stress levels. In such leaf springs, the seat portion does not rotate during spring deflection and the axle associated with the spring maintains a constant caster angle during jounce and rebound.
Although constant caster is often desirable, in some instances varying caster is optimal. Those skilled in the art will recognize that in trailing arm suspensions varying caster is often desirable in those instances when the axle, or its housing, is generally resistant to torsion. In those cases, by varying the caster angle of the axle during jounce and rebound, roll stability for the vehicle is increased. Therefore, the use of auxiliary roll stabilizers might be unnecessary. Elimination thereof reduces the cost and weight associated with those suspension systems.
In light of the aforementioned deficiencies of stress tolerant symmetrical leaf springs, it is desirable to design a symmetrical leaf spring that has cantilevers with substantially different spring rates so that the axle has varying caster during jounce and rebound.
As will be appreciated by those skilled in the art, vehicles often optimally have a biased, fixed caster for each of its axles. Different axles often have different desirable biased, fixed caster angles. In conventional suspension systems, and referring to FIG. 3, a caster wedge 28 is often positioned between the axle seat of the leaf spring and the axle to provide for the selected, fixed caster angle of the axle.
FIG. 3 illustrates a conventional suspension system used for a front steering axle 30. As shown therein, a vehicle frame 32 extends longitudinally and is suspended above axle 30 by a suspension system generally identified by reference numeral 34. The suspension system 34 includes a leaf spring 36 pivotally connected at one end to a hanger 38, which, in turn is fixedly mounted to frame 32. At its other end, leaf spring 36 is pivotally connected to a hanger 40 through a conventional shackle 42. Hanger 40 is mounted to frame 32. An air spring 44 is optionally mounted at its top side to an air spring mounting bracket 46, which is fixedly mounted to frame 32. Air spring 44 is seated on an axle attachment assembly 48 in alignment with axle 30. The axle attachment assembly 48 includes a pair of guide plates 50, 52 positioned on opposite sides of axle 30, the caster wedge 28, and a pair of U-bolts 54, 56 to fasten the assembly components together.
Caster wedge 28 causes axle 30 to rotate a fixed amount of degrees (either clockwise or counter-clockwise, depending on the orientation of the caster wedge) to accommodate the desired fixed caster angle for the axle. Use of extra suspension system components, such as caster wedge 28, adds weight to the suspension system and increases the costs associated with the design, assembly and service of such systems.
In light of the foregoing, it is desirable to design suspension system components, particularly leaf springs, that provide for the desired fixed caster angle of a vehicle axle.
As an object of the present invention, it is desirable to produce an optimally designed asymmetrical leaf spring that maintains a constant caster angle for its associated axle during jounce and rebound.
As another object, it is desirable to produce an optimally designed symmetrical leaf spring that produces a varying caster angle for its associated axle during jounce and rebound.
It is also desirable to reduce the expense associated with suspension systems used in vehicles.
It is further desirable to eliminate the necessity of including additional components in such suspension systems.
It is yet further desirable to design a leaf spring having built-in features to produce a select biased caster angle for its associated axle.
These and other objects of the preferred forms of the invention will become apparent from the following description. It will be understood, however, that an apparatus could still appropriate the invention claimed herein without accomplishing each and every one of these objects, including those gleaned from the following description. The appended claims, not the objects, define the subject matter of this invention. Any and all objects are derived from the preferred forms of the invention, not necessarily the invention in general.
The present invention is directed to a leaf spring assembly for use as an active component in vehicle suspension systems. The leaf spring assembly includes a full-leaf leaf spring component and a half-leaf leaf spring component. The full-leaf leaf spring extends substantially the entire length of the leaf spring assembly and the half-leaf leaf spring extends substantially the entire length of one of the cantilevers. The half-leaf leaf spring preferably also extends along the axle seat portion of the other cantilever and terminates at the end of the axle seat portion included within the other cantilever. The full-leaf leaf spring and the half-leaf leaf spring are preferably connected together by a fastener.
In a preferred form, when the leaf spring assembly has front and rear cantilevers of substantially unequal length, the half-leaf leaf spring extends substantially along the entire length of the shorter cantilever to soften that cantilever. Under such circumstances, the leaf spring assembly preferably has relatively uniform stress tolerance provides for a constant caster angle for its associated axle during deflection of the assembly due to jounce and rebound.
In another preferred form, when the leaf spring assembly has front and rear cantilevers of substantially equal length, the half-leaf leaf spring softens the cantilever along which it extends. Under these circumstances, the leaf spring assembly preferably has relatively uniform stress tolerance and provides for a varying caster angle for its associated axle during deflection of the assembly due to jounce and rebound.
In yet another preferred form, the axle seat portion of the full-leaf leaf spring is designed such that it biases the position of the axle associated with the leaf spring assembly to a predetermined caster angle. In that regard, one of the upper and lower surfaces of the full-leaf leaf spring, most preferably the lower surface, tapers throughout the axle seat portion in such a manner that the full-leaf leaf spring is thicker at one end of its axle seat portion than it is at the other end of its axle seat portion. In particular, throughout the axle seat portion, the upper and lower surfaces of the full-leaf leaf spring extend in the intersecting planes. As such, the full-leaf leaf spring, and therefore the leaf spring assembly, includes a built-in caster wedge that biases its associated axle to a predetermined caster angle.